Ultrasonic imaging has rapidly become a preferred modality for the non-invasive investigation of human tissues. Its non-ionizing character, moderate requirements in terms of signal processing and computation support, compactness, and continuing progress in image all favor the use of ultrasound whenever conditions permit. Thus, with the exception of body areas which are subject to uncontrolled multiple reflections (e.g. in the skull) and areas which fundamentally possess poor sonic transmission characteristics (e.g. the lungs), most areas of the body have been successfully made the subject of ultrasound diagnosis or screening. Some systems are multipurpose in essence, such as real time or B-scan body scanners and fetal monitors, while others are highly specialized, such as pulsed Doppler carotid imagers and flow monitors.
Recently, scientific and clinical data have been produced which provide strong indication of the efficacy of ultrasound scanning and imaging to screen, detect, and diagnose lesions in the human breast. In particular, it appears that appropriately directed and controlled B-scan images of a human breast permit detection of lesions in the 1 to 2 millimeter range and discrimination of malignancies in the 5 millimeter range based solely on ultrasound image. Further, such screening appears feasible at statistical levels of confidence comparable to those achieved through utilization of ionizing radiation (i.e., X-ray mammography). Such efficacy, together with ultrasound's apparent hazard-free nature, makes ultrasound a likely preferred mordality for large scale screening programs for early detection of breast cancer.
Ultrasonic diagnosis of the human body using large aperture pulse echo ultrasound imaging techniques have been described in, for example, U.S. Pat. Nos. 4,131,021 and 4,131,022 to Mezrich et al. Accordingly, such devices use a scanning transducer and an associated sonic lens submerged in water. The subject is positioned on an examination table over the water enclosure. Sonic energy from the transducer is transmitted through the water, focused by the sonic lens through the examination table and into the patient. Echoes are transmitted back in similar fashion. When diagnosing the condition of the human breast, it has been found desirable to eliminate the examination table from the transmission path and to transmit ultrasonic energy directly to the breast.
In certain instances, it has been found desirable to examine the human breast while it is suspended in the water. Thus, it is necessary to condition the water used for the ultrasound transmission medium to remove sources of interference that could distort the ultrasound image. When conditioning may involve filtering particulate matter, deaerating the medium, maintaining proper water level, maintaining uniform temperature to eliminate thermal gradients, and inhibiting bacterial growth to minimize interference with the ultrasound transmissions. It is also important to maintain the temperature of the water at a proper level so that the patient experiences no discomfort when the breast is introduced into the water.
It is also desirable, from an aesthetic and sanitary point of view, to be able to change the water in which the breast is suspended after every patient, or at least after every several patients. A problem has existed which made frequent water changing impractical because the water had to be properly conditioned to be used as a transmission medium for the ultrasound system. Proper conditioning of the water, however, can take a significant amount of time so that previous breast scanning devices have had significant limitations on the ability to change water frequently. The present invention addresses these problems and provides an efficient, water maintenance system for an ultrasound mammary scanning apparatus.